Printing press film sensor

ABSTRACT

An improved sensor has been provided for measuring the thickness of the film of dampening fluid on one of the rolls in the dampening mechanism of a lithographic printing press. The sensor comprises a capacitor formed between a sensor roller which runs in contact with the dampener form roll and a capacitor plate disposed concentric with the roller. The sensor roller which runs in contact with the dampener form roll has a film of dampening fluid thereon the thickness of which is dependent upon the thickness of the film of fluid on the dampener form roll. The sensor senses the change in capacitance of the capacitor which results primarily from the change in the dielectric of the space between the capacitor plate and the roller. The changes in the dielectric result from changes in the thickness of the film of dampening fluid on the roller. A frame is provided to support the capacitor plate and the sensor roller and the frame minimizes vibration between the roller and the capacitor plate to thereby provide an accurate sensor.

United States Patent 1191 Dauterman 1 May 1, 1973 [54] PRINTING PRESS FILM SENSOR [75] Inventor: Walter E. Dauterman, Willowick, Prlmary yde I. Coughenour Ohio Attorney-Y0unt and Tarolh [73] Assignee: Harris-intertype Corporation, [57] AESTRAT Cleveland Ohm An improved sensor has been provided for measuring [22] Filed: June 10, 1970 the thickness of the film of dampening fluid on one of v [211 App]. No: 45,119 the rolls in the dampening mechanism of a lithograph1c printing press. The sensor-comprises a capacitor formed between a sensor roller which runs in con- [52] US. Cl. ..-;...101/148, 101/350, 317/246, tact with the dampener form roll and a capacitor plate 324/61 P disposed concentric with the roller. The sensor roller [51] Int. Cl. .B41l 25/00, H()1g 5/20, GOlr 27/26 which runs in contact with the dampener form roll has [58] Field of Search ..324/61TK; 101/147, a film of dampening fluid thereon the thickness of 101/148, 350; 317/246 which is dependent upon the thickness of the film of fluid on the dampener form roll. The sensor senses the [56] References Cit d change in capacitance of the capacitor which results primarily from the change in the dielectric of the UNITED STATES PATENTS space between the capacitor plate and the roller. The 3,227,951 1/1966 Dykaar ..324/61 Changes in the dielectric result from changes in the 3 191 52 19 5 jorgensennn 10 /148 thlCkllCSS Of the Of dampening on the roller. 3,412,677 11/1968 Kant or ....101/148 A frame is Provided to pp the Capacitor P and 2,103,254 12/1937 Goedike ....101/148 the sensor roller and the frame minimizes vibration 3,094,065 6/1963 Roberts ....101/148 between the roller and'the capacitor plate to thereby 3,146,706 9/1964 7 Tonkin et al. 101/148 provide an accurate 11301; 3,499,383 3/1970 Southam ....l0l/l48 3,584,579 6/1971 Rothenberg .l ..lO1/35() 2 Claims, 6 Drawing Figures COMPARATOR Patented May 1, 1973 2 Sheets-Sheet l OSCILLATOR lA/I/EA/TOR W41. T5? 15. DA U T ERA/IAN ATTORNEYS FIGZ PRINTING PRESS FILM SENSOR The present invention relates to a printing press and more specifically to sensing means associated with a dampener mechanism in a printing press for measuring the fluid film thickness on one of the rolls in the dampeningtrain.

In a lithographic printing press ink and ink repellant fluid are applied to the plate cylinder of a press. As is well known, the ink flows onto certain portions of the printing plate disposed on the plate cylinder and the ink repellant fluid flows onto other portions of the plate. The control of the amount of ink repellant fluid that is directed to flow onto the' plate of the plate cylinder is important to good printing and many methods have been utilized to attempt to provide accurate control of the ink repellant fluid.

Problems have been associated with sensors for sensing the flow of dampening fluid to the plate cylinder due to the vibration that is imparted thereto 1 from the operation of the printing press. The vibration is generally such that the sensor may yield erroneous measurements of the thickness of the ink repellant or dampening film.

ing a film of dampening fluid thereon the thickness of which is dependent on the film thickness of the dampening fluid on the dampener roll, a sensor capacitance plate disposed adjacent to the sensor roller to enable the sensor to measure the capacitance between the plate and the sensor roller, the capacitance of which is dependent on the film thickness of the dampening fluid ing the capacitance plate and rotatably supporting the roller and wherein the frame means provides for vibration of the capacitance plate and the sensor roller as a unit so that vibrating relative movement of the roller and the plate is minimized and accurate measurement of the film thickness of the dampening fluid may be made. I g

A still further object of the present invention is to provide a new and improved sensor for measuring the film thickness of dampening fluid on the dampening roll of a printing press including a sensor roller formed from an electrically conductive material for rotating in engagement with the dampener roll and which receives an amount of dampening fluid thereon which is dependent on theamount ofdampening fluid that the dampener roll transfers to the plate cylinder of the printing press, an arcuate capacitor plate member disposed concentric to the roller and which cooperates with the sensor roller to form a capacitor for measuring the capacitance of the space between the plate and the sensor roller, the dielectric of which is changing due to the variance in the film thickness of dampening fluid on the sensor roller and frame means for supporting the roller and the concentric capacitor plate so that the-plate and the roller vibrate as a unit to thereby minimize vibration induced relative movement therebetween so that accurate measurements substantially free from vibration induced error of the film thickness of the dampening fluid may be made.

Another object of the present invention is to provide in a printing press a new and improved sensor for measuring the film thickness of fluid on a fluid transfer roll of a printing press, the sensor including a sensor roller having a first portion thereof for rotating in engagement with the roll and which receives an amount of dampening fluid thereon the film thickness of which is dependent upon the amount of dampening fluid that the roll transfers to the plate cylinder of the printing press and a second portion which is recessed so that dampening fluid is not transferred thereto to provide a reference surface free of dampening fluid. 7

Still another object of the present invention is to provide in a printing press a new and improved sensor for measuring the film thickness of dampening fluid on a transfer roll of the ink train of the printing press-and wherein the film thickness of the dampening fluid sensed on the transfer roll of the ink train is dependent upon the amount of dampening fluid applied to the plate cylinder of the press so that the sensor may render an indication of the amount of dampening fluid being applied to the plate on the plate cylinder of the press.

Further objects and advantages of the present invention will become apparent from the following description of a preferred embodiment of the present invention made with" reference to the accompanying drawings forming a part of the specification and wherein:

FIG. 1 is a side fragmentary view of a portion of a printingpress embodying the present invention illustrating the plate cylinder, the dampener mechanism, a portion of the ink train and the sensor;

FIG. 2 is a side. view of the roll and capacitor assembly which is disposed contiguous to the dampener form roll; 7

FIG. 3 is a top view of the roller and capacitor assembly taken approximately along lines 3-3 of FIG. 2;

FIG. 4 is a schematic side viewtaken approximately along the lines 4-4 of FIG. 1 illustrating the relative length of the sensor roll and the dampener form roll;

FIG. 5 is a side view of another embodiment of the present invention showing a modified sensor assembly and the schematic circuitry associated therewith; and

FIG. 6 is a schematic side fragmentary view of a portion of the printing press illustrating the sensor utilized in conjunction with an ink form roll of the inker train.

The present invention relates to an apparatus for sensing the amount of ink repellant fluid or dampening fluid applied by a dampening mechanism to the plate of a lithographic printing press. The ink repellant fluid is preferably water or a mixture of water and alcohol and is transferred from a fluid reservoir to a dampener form roll which runs in contact with the plate cylinder. A capacitor roller rotates in engagement with the dampener form roll and a film of water flows onto the surface thereof which has a thickness which is dependent on the thickness of the film of water on the dampener form roll. A capacitor plate is disposed adjacent to the capacitor roller and is supported by a frame which supports the capacitor roller. The capacitor plate and the capacitor roller form a sensor for measuring the capacitance of the space between the plate and the capacitor roller. The capacitance of the space changes as the thickness of the film of water varies. Thus, by sensing the capacitance between the capacitor roller and the capacitor plate, the amount of water which is being transferred to the plate cylinder can be sensed. The frame and the mounting which support the capacitor roll and the capacitor plate is a rigid frame and minimizes vibratory relative movement between the capacitor plate and the capacitor roll.

Referring to FIG. 1, a plate cylinder of a litho- 8 graphic printing press is shown associated with a dampening mechanism 12 and an inking mechanism 13, both of which are schematically illustrated.

The dampening mechanism 12 includes a transfer or pan roll 16 which is associated with a fluid reservoir 14 which is filled with a dampening fluid which is preferably water or a mixture of water and alcohol. The pan roll 16 rotates in a counterclockwise direction and rotation of the pan roll 16 through the fluid reservoir 14 effects the formation of a film of dampening fluid on the surface of the pan roll 16. The pan roll 16 rotates in contact with the surface of a metering roll 18 and the surface of a dampener form roller 20. The surfaces of the metering roll 18 and the dampener form roll 20 are adjusted in pressure relationship with the surface of the pan roll 16. Adjustment of pressure between the metering roll 18 and the pan roll 16 meters and smoothes the film of dampening fluid which is transferred to the dampener form roll 20. The dampener form roll 20 transfers a film of dampening fluid to the surface of the plate cylinder 10 which has a lithographic printing plate 24 thereon.

Ink is supplied to the plate cylinder l0'by the inking mechanism 13 which includes an ink form roll 22 which rotates in engagement with an ink vibrator roll 27. The ink vibrator roll 27 is associated in a wellknown manner with the supply of ink and transfers the ink from the ink supply to the ink form roll 22. As is well known, the ink vibrator roll 27 shifts longitudinally to effect the applicationof a film of ink having a substantially uniform thickness to the ink form roll 22. The ink form roll rotates in engagement with the plate cylinder 10 and transfers ink to the plate 24 thereon.

As is illustrated in FIG. 1, a sensor 26 is associated with the dampener form roll 20 and is operable to measure the thickness of a film of dampening fluid on the surface of the dampener form roll 20. The sensor 26, which is more fully illustrated in FIGS. 2 and 3, includes a roller 28 mounted to roll in contact with the dampener form roll 20. The dampener form roll 20 preferably has a molleton or rubber surface thereon and the'roller 28 preferably has a chrome surface 48 thereon treated to make it receptive to the dampening fluid on the dampener form roll 20. As the roller 28 rolls in contact with the dampener form roll 20, a film of water will be transferred to the chrome surface 48 of the roller 28. The thickness of the film of water which is transferred to the roller 28 will be a function of the thickness of the film of water on the dampener form roll 20 at the roller 28. The thickness of the film of dampening fluid or water on the dampener form roll 20, when it leaves the plate and on the roller 28; will depend on the amount of water which is transferred to the lithographic plate 24 on the plate cylinder 10. Thus, the film thickness of the water on the surface 48 of the roller 28 is an indication of the amount of water which is being transferred to the lithographic printing plate 24 on the plate cylinder 10.

Supported adjacent to the roller 28 is a capacitor plate 30. The capacitor plate 30 includes a concentric surface 50 which is concentric to the surface 48 and the axis of rotation of the roller 28.'The roller 28 and the capacitor plate 30 form a capacitor with the surface 48 of the roller 28 forming one plate of the capacitor and the concentric surface 50 of the' capacitor plate 30 forming the other plate of the capacitor. If a film is to be sensed on a roll or cylinder with a hard surface thereon rather than the rubber surface of the dampener form roll 20, the sensor roller 28 may be covered with a soft, thin covering having a known dielectric when dry. The capacitor formed between the roller 28 and the plate 30 has a capacitance which varies and the change in the capacitance results from the change in the dielectric due to the amount of dampening fluid between the metal surface of the roller 28 and the plate 30.

The dielectric of thecapacitor is measured between the surface 50 of the plate 30 and the surface 48 of the roller 28. Thus, the dielectric of this capacitor consists of the dielectric of the dampening fluid on the surface 48 of the roller 28 plus the dielectric of the air gap between the surface 50 of the capacitor plate 30 and the surface of the dampening fluid on the roller 28. The dielectric constant of the dampening fluid will be sub stantially higher than the dielectric constant of the air and the capacitance of the capacitor will vary depending upon how much of the space between the surface 50 of the plate 30 and the surface 48 of the roller 28 is occupied by dampening fluid and how much is occupied by air. Thus, it should be apparent that by sensing the capacitance of the-capacitor, the film thickness of dampening fluid on the roller 28, can be measured. The flow of dampening fluid to the plate cylinder 10 can also be measured since the flow .of dampening fluid to the plate cylinder 10 is a function of the thickness of the fluid on the roller 28.

The roller 28 is rigidly supported on a rigid shaft 32 joumaled at both of its ends in a frame 52. The shaft 32 and its mounting rigidly supports the roller 28 against radial or axial movement relative to the frame 52. The roller 28 is a short roller, as illustrated in FIG. 4, and has an axial length which is substantially less than the axial length of the dampener form roll 20. The small size of the roller 28 minimizes deflections of the roller 28 which could cause erroneous sensing of the thickness of the film of dampening fluid if the deflections varied the spacing between the capacitor plate 30 and the roller 28.

The capacitor plate 30 is mounted on a sheet of insulating material 54 which preferably may be material such as fiberglass or plexiglass. The insulating material 54 insulates the capacitor plate 30 from the frame 52. Set screws 36 extend into the sheet of insulating material 54 and do not contact the capacitor plate 30. The set screws 36 fix the plate 30 relative to the frame 42. The screws 36 are disposed in elongate slots 56 in the side of the frame member 52. The elongate slots 56 enable the plate 30 to be adjusted relative to the roller 28 to thereby vary the spacing between the surface 48 of the roller 30 and the surface 50 of the concentric plate 30.

A screw assembly 42 is provided on a cross member of the frame 52. The screw assembly 42 includes a threaded body portion 44 having an end portion 46 which engages with the top surface of the insulating member 54. By rotating the head 47 of the screw assembly 42, the plate 30 can be adjusted relative to the roller 28. When the plate is adjusted to its correct position, the bolts 36 will be tightened to the frame 52 and relative movement between the frame 52 and the capacitive plate 30 will be prevented. I

An oscillator detector circuit 58 is schematically illustrated in FIG. 1 and is operable to sense the capacitance of the capacitor formed between the surface 50 of the plate 30 and the surface 48 of theroller 28. The oscillator detector circuit 58 is a tuned circuit which is connected to the sensor 26 and operates in a well-known manner to measure capacitance. It should be understood that, for any selected spacing between the plate 30 and the roller 28, the circuit 58 can be tuned by varying the component parts thereof and balancing of the circuit can be performed by routine adjustments. The output signal of the oscillator detector circuit 58 will be dependent on the dielectric of the space between the metal surface 50 of the capacitor plate 30'and the surface 48 of the roller 28 and will be indicative of the film thickness of dampening fluid being'applied to the plate cylinder 10. Thus, the sensor 26 and the detector circuit 58 will be operable to indicate the amount of dampening fluid being applied to the plate 24 on the plate cylinder 10.

The output of the detector circuit 58 can'be used to vary the operation of the dampener mechanism 12 in known ways to enable the dampening mechanism to provide a predetermined amount of dampening fluid to the plate cylinder 10. For example, if the amount of dampening fluid being applied to the plate cylinder is too small, the speed of a motor'M which effects rotation of the pan roll 16 can be increased, conversely, if

too great, the speed of the motor can be reduced to effect a smaller amount of fluid being applied thereto.

It should be apparentthat the sensor 26 is free from vibrational induced inaccuracies. This is due to the fact that the capacator plate is rigidly mounted on .the frame 52 along with the roller 28. Thus, while vibrations might be imparted to the sensor 26, the capacitor plate 30 and the roller 28 will vibrate as a unit and vibratory relative movement between the plate 30 and' the roller 28 will be minimized due to the fact that the frame member 52 will rigidly support both the-roller 28 and the capacitor plate 30. Therefore, it should be apparent that changes in the spacing of the surface 48 of thereto, the thickness of which is a function of the film thicknessof the dampening fluid on the plate cylinder. The roller 84 also includes a second surface portion 82 the amount of fluid flowing to the plate cylinder 10 is which is located inwardly of the first surface portions 80 and which does not have a film of dampening fluid transferred thereto. A pair of capacitor plate members are located adjacent to the first surface portions of the roller 84. The capacitor plates 70 preferably have a concentric configuration and form capacitors between the surface portions of the plate 70 and the surface portions 80 of the roller 84. The capacitance which is sensed by the capacitors formed between the capacitor plates 70 and the surface portions 80 of the roller 84 will vary and the variance of the capacitance will result primarily from the changes in the dielectric of the capacitor which is due to changes in the film thickness of the dampening fluid on the portions 80 of the roller 84. The capacitor formed between the plates 70 and the portions 80 of the roller will operate in'an analogous fashion to the capacitor formed between the capacitance plates 30 and the roller 28 illustrated in FIGS. 1 to 4.

The capacitance plates 70 are disposed on a plate of insulating material 72 such as plexiglass which will insulate the capacitance plates from the frame 52 which supports the insulating member 72. A pair of adjustment screws 78 are disposed on a cross member of the frame 52 and engage with the insulating member 72. Rotation of the adjustment screws 78 will effect the ad-' justment of the spacing between the capacitance plates 70 and the surface portions 80 of the roller 84.

A capacitance plate 74 is also connected with the insulating member 72 and is disposed adjacent to the second portion 82 of the roller 84. The capacitance plate 74 will cooperate with the surface portion 82 of the roller 84 to form a capacitor therebetween whose capacitance will reflect the spacing between the surface of the plate 74 and the surface portion 82 of the roller 84. The capacitance will be dependent upon the spacing between the surface 82 and the plate 74 and will not be dependent upon the film thickness-of the dampening film-due to the fact that there will be no dampening film on the surface portion 82 of theroller The capacitor plate 84 is secured to the insulating plate .72 by an adjustable screw means 76 which operates in a manner analogous to the manner of operation of the adjustable screw means 78.-The screw means 76 will be operable to position the capacitance plate 74 relative to the surface 82 of the roller 84 so that the position of the capacitor plate 74 may be adjusted relative to the surface portions 82 of the roller 84 without disturbing the spacing between the capacitor plates 70 and the surface portions of the roller 84.

The capacitance of the capacitor formed between the surface of the plates 70 and the surfaces 80 of the roller 84 will be dependent upon the spacing between the surface portions 80 and the plates 70 and the film thickness of the dampening fluid on the surface portions 80 of the roller 84. The capacitance of the capacitor formed between the plate 74 and the surface portion 82 of the roller 84 will be dependent upon the spacing between the plate 74 and the surface portion 82 of the roller 84. While the roller 84 and the capacitor plates 70 and 74 are rigidly secured to the frame 72 to hold them against relative vibration, there is a possibility in a change in spacing between the capacitor plates 70 and 74 and the surface portions of the roller 84 due to contraction or expansion of the roller 84. The problem of the change in spacing sometimes may occur when a dampening fluid such as water and alcohol is used in which case the water and alcohol which flow over the surface portions of the roller 84 so as to cool the roller 84 sufficiently to cause a change in diameter thereof.

The embodiment illustrated in FIG. eliminates erroneous measurementsof the dampening film thickness caused by a change in diameter of the roller 84. The change in capacitance of the capacitor formed between the capacitor plate 74 and the surface portion 82 of the roller 84, which is dependent upon changes in the diameter of the roller 84, is compared with the changes in capacitance of the capacitor formed between the capacitor .plates 70 and the surface portions 80 of the roller 84, which is dependent upon the changes in diameter of the roller 84 and the changes in the film thickness of the dampening fluid on the surface portions 80 of the roller.

Asis illustrated in FIG. 5, the change in capacitance between the capacitor plates 70 and the surface portions 80 of roller 84 is sensed by a detector circuit 86 which operates much in the same manner as the detector circuit 58 illustrated in FIG. 1. The changes in capacitance between the capacitor plate 74 and the surface portion 82 of the roller 84 is sensed by a detector circuit 88. The output of the detector circuit 86 and the detector circuit 88 is then compared by a comparator circuit 90 to obtain the difference as the capacitor signal. The comparator circuit 90 operates to correct error in the detector circuit 86 due to changes in the diameter of the roller 84. Moreover, if relative movement between the capacitor plates and the roller takes places as a result of vibration, the comparator circuit 90 will operate to correct the erroneous signals which will be sensed by the capacitor formed between the capacitor plate 74 and the surface portion 82 so that accurate measurements of the dampening film thickness may be sensed.

Thus, the embodiment illustrated in FIG. 5 operates in a manner substantially analogous to the operation of the sensor 26 illustrated in FIGS. 1 to 4. However, the sensor illustrated in FIG. 5 is operable to correct errors in the output signals of the detector circuits due to contraction or expansion of the sensor roller.

While the sensor has been shown in FIGS. 1-5 as measuring the film thickness of dampening fluid at the damper form roll adjacent to the plate cylinder, it should be apparent that the sensor 26 could be associated with other rolls for transferring dampening fluid or ink to the plate. For example, as is schematically illustrated in FIG. 6, the sensor could be utilized to run in contact with one of the transfer rolls in the ink train 13. As is illustrated in FIG. 6, the sensor 26 is in engagement with the ink form roll 22 of the ink train 13. The ink train 13, only a portion of which is illustrated, includes the ink form rolls 22 and 92, the ink vibrator roll 27, and an ink transfer roll 96 which cooperate in a well known manner to transfer ink from the ink supply, not illustrated, to the plate 24 on the plate cylinder 10. In a lithographic press the application of dampening fluid such as water to the plate either directly or through the ink train results in a transfer of some of the water back through the ink train itself. The

amount of water transferred back through the ink train varies, decreasing as the water in the ink train is farther from the supply of water, due to evaporation. However, under equilibrium conditions, the amount of water at any one point in the ink train is dependent upon the amount of water being transferred to the plate on the printing cylinder. Thus, by measuring the water on the surface of one of the ink form rolls a measure of the water flowing to the plate may be had.

The sensor 26, illustrated in FIG. 6, in engagement with the ink form roll 22 has the outer surface of the roll 28 treated to make the surface hydrophilic so that the surface will repel ink therefrom while picking up a water film from the ink form roll 22. The amount of water onthe ink form roll 22 will be dependent upon -the amount of water on the plate 24 and the film thickness of the water on the sensor roll 28 will be dependent on the amount of water on the ink form roll 22. Thus, a film of water, the thickness of which is dependent on the amount of water being applied to the plate 24 on the plate cylinder 10, will be present on the surface of the sensor roll 28. The sensor 26 will be operable in a manner described hereinabove to sense the thickness of this water film thereon independently of the amount of ink present on the ink form roll to thereby render an indication of the amount of water on the plate cylinder.

From the foregoing, it should be apparent that the printing press with a new and improved sensor for sensing the dampening film thickness at one of the rolls in the dampening train of an offset printing press has been provided. The sensor 26 is constructed to form a capacitor between a roller and a plate member which is mounted relative to the roller so as to be relatively free of vibratory movement therebetween. The sensor senses the capacitance between the plate and the roller which varies as the film thickness of the dampening fluid varies. By measuring the capacitance, the amount of the dampening fluid being applied to the plate cylinder 10 can be accurately measured. I -WhatIclaimis: v

1. In a printing press having a dampening mechanism for applying'water to a plate on a plate cylinder and an inker mechanism having ink transfer means for transferring ink from an ink supply to the plate on the plate cylinder and which transfer'means has water thereon the amount of which is dependent upon the amount of water being transferred to the plate by the dampening mechanism, a sensor for measuring the amount of fluid transferred to the plate comprising means having a hydrophilic surface thereon for engaging with the ink transfer means and adapted to have a film of water transferred thereto the thickness of which is dependent upon the amount of water on the transfer means'and the amount of water being transferred to the plate cylinder, and means associated with said hydrophilic surface for measuring the film thickness of the water on said hydrophilic surface and to render an indication of the amount of 'water being transferred to the plate cylinder, said means having a hydrophilic surface thereon comprising a sensor roller having an outer hydrophilic surface thereon, said ink transfer means comprises an ink form roll, said sensor roller being adapted to have said hydrophilic surface thereof rotatably engage with said ink form roll to pick up a film of water from said ink form roll and said means associated with said hydrophilic surface comprising a capacitance plate disposed adjacent to said hydrophilic surface of said sensor roller, said sensor roller and said capacitance plate forming a capacitor for sensing the film thickness of said water on said hydrophilic surface of said sensor roller, said sensor roller having a first surface portion thereon which is adapted to rotatably engage with said ink form roll and have a film of fluid transferred thereto which has a film thickness which is dependent on the film thickness of the dampening fluid which is transferred to the plate on the plate cylinder of the press and a second surface portion thereon which is 1 spaced from said first surface portion, said second sur face portion remaining free of said dampening fluid,

said capacitance plate being disposed adjacent to said first surface portion of said roller'and spaced apart from said second surface portion of said roller and further including a second sensor capacitance plate disposed adjacent to said second surface portion of said roller and spaced apart from said first surface portion of said roller for providing a reference signal. 2. In a printing press, a capacitance film sensor'as defined in claim 1 wherein said second capacitance plate and said second surface portion of said roller cooperate to forni a second capacitor for sensing changes in the spacing between said second capacitance plate and said second surface portion of said roller. Y i 

1. In a printing press having a dampening mechanism for applying water to a plate on a plate cylinder and an inker mechanism having ink transfer means for transferRing ink from an ink supply to the plate on the plate cylinder and which transfer means has water thereon the amount of which is dependent upon the amount of water being transferred to the plate by the dampening mechanism, a sensor for measuring the amount of fluid transferred to the plate comprising means having a hydrophilic surface thereon for engaging with the ink transfer means and adapted to have a film of water transferred thereto the thickness of which is dependent upon the amount of water on the transfer means and the amount of water being transferred to the plate cylinder, and means associated with said hydrophilic surface for measuring the film thickness of the water on said hydrophilic surface and to render an indication of the amount of water being transferred to the plate cylinder, said means having a hydrophilic surface thereon comprising a sensor roller having an outer hydrophilic surface thereon, said ink transfer means comprises an ink form roll, said sensor roller being adapted to have said hydrophilic surface thereof rotatably engage with said ink form roll to pick up a film of water from said ink form roll and said means associated with said hydrophilic surface comprising a capacitance plate disposed adjacent to said hydrophilic surface of said sensor roller, said sensor roller and said capacitance plate forming a capacitor for sensing the film thickness of said water on said hydrophilic surface of said sensor roller, said sensor roller having a first surface portion thereon which is adapted to rotatably engage with said ink form roll and have a film of fluid transferred thereto which has a film thickness which is dependent on the film thickness of the dampening fluid which is transferred to the plate on the plate cylinder of the press and a second surface portion thereon which is spaced from said first surface portion, said second surface portion remaining free of said dampening fluid, said capacitance plate being disposed adjacent to said first surface portion of said roller and spaced apart from said second surface portion of said roller and further including a second sensor capacitance plate disposed adjacent to said second surface portion of said roller and spaced apart from said first surface portion of said roller for providing a reference signal.
 2. In a printing press, a capacitance film sensor as defined in claim 1 wherein said second capacitance plate and said second surface portion of said roller cooperate to form a second capacitor for sensing changes in the spacing between said second capacitance plate and said second surface portion of said roller. 